In butterfly valves, translational movement of the valve plate relative to the pivot mechanism can be used to effect dynamic torque balancing, and to facilitate actuation by using the torque exerted by fluid on the plate to rotate the latter. To applicants' knowledge, these principles were first set forth in the above-referenced patent application, Ser. No. 374,897, filed on June 30, 1989. They are schematically illustrated in FIGS. 12A-12C of the present application, wherein numerals 20, 22, 24, 26, and 28 indicate a valve plate, a pivot shaft, a duct, a bracket intersecuring the shaft and plate, and the direction of flow respectively. Arrow 30 and numeral 32 indicate the center of pressure associated with the forces exerted by fluid on the plate 20, and the pivot axis about which the plate is pivotable.
In FIG. 12A, the shaft 22 is centered in relation to the longitudinal dimension of the plate 20 and the plate is in a closed position. The center of pressure 30 is aligned with the pivot axis 32, so the net torque exerted by the fluid on the plate 20 is zero. If the plate 20 is rotated to an open position as illustrated in FIG. 12B, and translated relative to the shaft 22 so that the center of pressure 30 is aligned with the pivot axis 32 as illustrated in FIG. 12C, then the plate is effectively torque-balanced and the flow rate associated with the rotational angle 34 can be maintained with minimal input force required from the actuator 36. If the translational movement is too limited in range to achieve torque balancing at all rotational positions of the plate 20, it can still be used to advantage in minimizing the net torque exerted by the fluid, thus still minimizing the input force required from the actuator 36.
If it is desired to change the rotational angle 34, then the plate 20 can be translated relative to the shaft 22 in the appropriate direction to effect a misalignment of the center of pressure 30 with the pivot axis 32, thus increasing the net fluid dynamic torque, and the force required to effect the change is exerted in whole or in part by the fluid conveyed in the duct 24.
Butterfly valves such as those described above can be beneficially used in a variety of applications such as aircraft, spacecraft or space stations, oil pipelines, and process pipelines generally, to name a few. The primary benefit to be derived in a specific application may differ from that to be derived in another, although all such benefits are attributable to the reduction of fluid dynamic torque. For example, reductions in weight, volume, and/or energy usage (all resulting from the use of smaller actuators) may be the primary benefits associated with aerospace vehicles, whereas a reduction in valve failures attributable to high torque loads may be a primary benefit associated with process pipelines.